Rayleigh scattering – en

Rayleigh scattering is a type of scattering that occurs when electromagnetic waves, such as light, encounter particles or obstacles much smaller than the wavelength of the incident wave. This phenomenon is named after the British physicist Lord Rayleigh, who first described it in the late 19th century.

In Rayleigh scattering, the intensity of the scattered light is inversely proportional to the fourth power of the wavelength (I ∝ 1/λ^4). This means that shorter wavelengths (e.g., blue and violet light) scatter more efficiently than longer wavelengths (e.g., red and yellow light). However, our eyes are more sensitive to blue light than violet light, so we perceive scattered light as predominantly blue.

Rayleigh scattering is responsible for several optical phenomena observed in nature:

1. Blue sky: The blue color of the sky during the daytime is a result of Rayleigh scattering. As sunlight passes through the Earth’s atmosphere, the shorter wavelengths (blue and violet) scatter more than the longer wavelengths (red and yellow). This scattered blue light is what we perceive as the color of the sky. On the other hand, the direct sunlight that reaches us appears yellowish because the shorter wavelengths have been preferentially scattered away.
2. Red and orange sunsets: During sunrise and sunset, the sun’s rays pass through a more significant portion of the Earth’s atmosphere, causing even more scattering of the shorter wavelengths. This leads to an increased proportion of the longer wavelengths (red, orange, and yellow) reaching the observer, resulting in the characteristic red and orange hues of sunrises and sunsets.
3. Twinkling of stars: The twinkling or scintillation of stars observed from the Earth’s surface is also partially due to Rayleigh scattering. As starlight passes through the Earth’s atmosphere, the light is scattered by air molecules, causing fluctuations in the intensity and color of the starlight reaching an observer.

Rayleigh scattering also has practical applications in various scientific fields, such as:

• Atmospheric science: Rayleigh scattering is used to study the composition and properties of the Earth’s atmosphere, as well as the radiation budget, which plays a crucial role in understanding climate change.
• Remote sensing: Rayleigh scattering is taken into account in remote sensing techniques that rely on the interaction of electromagnetic waves with the Earth’s surface and atmosphere, such as satellite imaging and Lidar.
• Spectroscopy: Rayleigh scattering is used as a reference in Raman spectroscopy, a technique that provides information about the vibrational modes of molecules, allowing for the identification and analysis of chemical compounds.

Understanding Rayleigh scattering and its effects is essential for interpreting various optical phenomena in nature and for various scientific and technological applications.

Scattering

Scattering of electromagnetic waves occurs when the waves encounter obstacles or particles in their path, causing them to change direction, spread out, or redistribute their energy. Scattering plays a crucial role in many areas of physics, including optics, atmospheric science, and remote sensing.

There are several types of scattering, depending on the size of the obstacles or particles relative to the wavelength of the incident electromagnetic waves:

1. Rayleigh scattering: This type of scattering occurs when the size of the particles or obstacles is much smaller than the wavelength of the incident electromagnetic wave. In Rayleigh scattering, the intensity of the scattered light is inversely proportional to the fourth power of the wavelength (I ∝ 1/λ^4). This means that shorter wavelengths (e.g., blue light) scatter more efficiently than longer wavelengths (e.g., red light). Rayleigh scattering is responsible for the blue color of the sky, as shorter wavelengths of sunlight scatter more in the Earth’s atmosphere, while the longer wavelengths pass through more directly and create the direct sunlight we see.
2. Mie scattering: Mie scattering occurs when the size of the particles or obstacles is comparable to the wavelength of the incident electromagnetic wave. Mie scattering is less dependent on the wavelength and can scatter light in all directions. This type of scattering is responsible for the white or gray appearance of clouds, as water droplets in the clouds scatter sunlight in all directions without a strong preference for shorter wavelengths.
3. Geometric or specular scattering: This type of scattering occurs when the size of the obstacles or particles is much larger than the wavelength of the incident electromagnetic wave. In this case, the wave interacts with the obstacles following the laws of geometric optics, such as reflection and refraction. Specular scattering is common on smooth surfaces like mirrors, glass, and calm water, where the angle of incidence is equal to the angle of reflection.
4. Multiple scattering: In some cases, electromagnetic waves can undergo multiple scattering events as they interact with a collection of particles or obstacles. This can lead to a more complex redistribution of energy and is often important in understanding phenomena like the greenhouse effect, where multiple scattering events involving greenhouse gases can trap heat in the Earth’s atmosphere.